The present invention relates to centrifugal pump assemblies, and more particularly to improvements in upright pump assemblies which may constitute the primary recirculating pump of nuclear reactor plants, for example, pressurized water reactors.
It is known to provide a centrifugal pump assembly for use in nuclear reactor plants with three coaxial shafts including a lower shaft or pump shaft, an upper shaft or motor shaft, and an intermediate shaft for the necessary radial and/or thrust bearings. The motor shaft is driven by a prime mover and rotates the intermediate shaft through the medium of a flexible coupling. The intermediate shaft rotates the pump shaft through the medium of a rigid coupling. In order to allow an attendant to gain access to the friction bearings and/or sealing elements for the pump shaft, the conventional assemblies normally employ a removable elongated insert which is secured in the pump assembly between the elements of the rigid coupling by two additional coupling elements. This insert and the additional coupling elements contribute to the overall length, bulk and cost of the pump assembly.